The catalyst containing molybdenum, bismuth, and iron is known as an oxidation catalyst which is used for producing an unsaturated aldehyde and an unsaturated carboxylic acid through gas-phase catalytic oxidation of propylene, isobutylene, tertiary butyl alcohol (hereinafter, sometimes expressed as “TBA”), or methyl tertiary butyl ether (hereinafter, sometimes expressed as “MTBE”).
For example, in Patent Documents 1 and 2, a method for producing a catalyst is individually disclosed, in which a mixed liquid containing a compound which becomes a raw material of the catalyst is prepared and the resultant mixed liquid is dried and then calcined.    Patent Document 1: Japanese Patent Application Laid-Open No. Hei 8-309,191    Patent Document 2: Japanese Patent Application Laid-Open No. Hei 8-309,192